This invention is directed to injection molding machines, and more particularly, to an securing and clamping assembly for use with the bars of both singular and tandem injection molding machines.
The prior art includes many types of tie bar gripping and clamping assemblies for use with injection molding machines. The gripping of the bars via these assemblies allows for a high clamping force to be applied to the mold halves during injection molding. Typical tie bar gripping and mold clamping mechanisms are shown in the patents to Fukuzawa et al., U.S. Pat. No. 5,135,385; Romi, U.S. Pat. No. 5,275,550; Hirata, U.S. Pat. No. 5,238,394 and Kushibe et al., U.S. Pat. No. 4,874,309. In each of these patents, a combination tie bar gripping mechanism mold clamping unit is disclosed wherein the tie bar is gripped via clamping devices moving transverse the longitudinal direction of the tie bars.
Accordingly, with reference to FIG. 5, Romi discloses the use of hydraulic clamps 9 and 10 for engaging circular grooves 18 of tie bar 17 for gripping the tie bars prior to the application of a clamping pressure via separate hydraulic cylinders 7. Similarly, Kushibe et al. discloses the use of halves 180 for clamping threads 172 of tie bar 164 so as to grip the tie bars prior to the application of a clamping force via separate hydraulic cylinders 160.
More particularly, the patent to Fukuzawa et al. discloses a clamping system which includes a fixed platen on one end of a machine base and a plurality of clamping cylinders wherein the fixed platen holds a fixed mold therein. A movable platen is fixed to the other end of the machine base and holds a movable mold therein, wherein a plurality of tie bars extend through the movable platen into the fixed platen. At one end of the tie bars, pistons are positioned wherein the pistons are slidably received within the clamping cylinders. In addition, the tie bars include screw threads or grooves on their end nearest the clamping cylinders. A unit is disposed between the movable platen and the fixed platen for moving the movable platen to and from the fixed platen. The movable platen includes two part nuts mounted therein for meshingly engaging additional screw threads or grooves positioned adjacent the end of the tie bar nearest the movable platen.
A further stopper mechanism is included in the movable platen which is engagable with recesses on the tie bars. The inner peripheral surfaces of the pistons include threads which are engageable with the screw threads or grooves on the tie bars adjacent the fixed platen. Accordingly, the pistons may be rotatable through means connected with a drive while engaged with the threads or grooves of the tie bars for adjusting the clamped position of the mold halves. Clamp position is adjusted by maintaining the female screw on the inner surface of the piston in meshed relationship with the screw portion at the end of the tie bar. By rotating the piston via a mechanism such as a sprocket and chain, the position of the mold halves can be adjusted as necessary. For this design, the threads on the inner surface of the piston are always maintained in meshed relationship with the threaded end of the tie bar and are used primarily for shut height adjustment.
Hirata discloses a mold clamping apparatus for a molding apparatus. The mold clamping apparatus includes a base, a fixed panel and a movable panel disposed on the base and respectively supporting mold halves. A plurality of tie bars each having a screw shaft at one end thereof pass through the movable panel toward the fixed panel. The plurality of clamping cylinders are disposed on the fixed panel for clamping another end of the tie bars when the mold apparatus is in a closed position. Each clamping cylinder includes cylinders 14 and semi-circular chucks 17 positioned transverse the longitudinal dimension of the tie bar. The cylinders 14 are actuated for gripping tie bar upon contact of the tie bar with a recess positioned in a primary piston of the clamping cylinder. Once cylinders 14 are engaged with tie bars 9, pressure can be applied to the primary piston 12 for providing the clamping force to the mold halves 25. The clamping apparatus further includes a mechanism for moving the movable panel towards and away from the fixed panel and an adjusting mechanism disposed on the movable panel, for simultaneously fixedly adjusting the axial position of the screws on the tie bar with respect to the movable panel so that molds of varying sizes can be accommodated. The secondary clamping pistons 14 and semi-circular chucks 17 are not rotatable into engagement with tie bars 9 and must be maintained in engagement with the tie bars during the application of pressure against primary cylinder 12.
The patents to Siegel, U.S. Pat. No. 3,183,555; Stubbe et al., U.S. Pat. No. 3,120,039 and Quere et al., U.S. Pat. No. 2,916,768 disclose further tie bar clamping mechanisms for use with molding machines. More particularly, Siegel discloses an expandable sleeve or bush 15 which envelopes the outer surface of a tie bar. The sleeve is adapted to engage inner walls of bores provided in a closing platen 9, wherein the bushes are adapted to receive guide columns or tie bars 4, such that the closing platen 9 is held on the guide columns by frictional contact. Stubbe et al. discloses the use of cylinders 21 having pistons 23 which are connected to levers 25 which in turn function to operate clamping jaws 26 for gripping shafts or tie bars 1. Quere et al. discloses the use of pistons for operating claws which rotate to grasp mating claws of tie bars moving from a movable platen 4 to stationary platen 7. The jaws are located in the stationary platen. Finally, European Patent 0290858 discloses the use of electromagnets 8 for clamping tie bar or column ends 7, for locking a movable tool clamping platen to a fixed tool clamping platen.
The patents to Schad et al., U.S. Pat. No. 5,185,119; Balevski et al., U.S. Pat. No. 4,090,837 and Lohman, U.S. Pat. No. 3,707,342, disclose different embodiments of tandem molding machines, i.e., wherein each machine has more than one mold. However, none of the tandem machines include tie bar securing/clamping mechanisms as discussed above or as disclosed in the present invention.
Schad et al. discloses an injection molding machine and method of operation having a plurality of accessory arrangements for molding a plurality of piece parts in efficient overlapping time cycle using primary and secondary molten plastic injection units, primary and secondary clamping units, and a plurality of injection units in various arrays including molding piece parts in reverse or uniform orientation. The tandem machine includes two fixed end platens and two center movable mold platens movable against and towards one of the fixed platens.
Lohman discloses a tandem injection molding apparatus having two molds, spaced apart with a dual nozzle injection unit positioned between the molds to fill the two molds alternately. The cooling periods of the two closed molds overlap in time and while one mold is cooling the other one is opened, emptied of its molded part, closed again and injected with a new charge of plastic. During the cooling period of one mold, the injection unit not only injects plastic into the other mold but also recharges for a new operating cycle. The machine includes a stationary side platen and movable center and other side platens.
There exists, therefore, a need for improved single mold and tandem mold injection molding machines having an improved tie bar securing/clamping assembly, wherein the securing/clamping assembly can be engaged and disengaged from the tie bar at each molding cycle.